这是我的Button声明,用.xaml文件编写:
<dxlc:LayoutGroup Orientation="Horizontal" Margin="5,15,0,5">
<Grid MinWidth="100">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Button
IsEnabled="{Binding IsSearchCriteriaHasValue}"
Content="Search"
MaxHeight="25"
MaxWidth="70"
ClipToBounds="True"
VerticalAlignment="Center"
HorizontalAlignment="Center"
HorizontalContentAlignment="Center"
VerticalContentAlignment="Center"
Command="{Binding SearchCommand}"/>
</Grid>
</dxlc:LayoutGroup>
无论用户是否在搜索按钮旁边的搜索框中键入了任何搜索文本,这都是返回true / false的函数。该函数位于另一个.cs文件中:
public bool isButtonEnabled
{
return (SearchBox.Selection.Count > 0);
}
问题是isEnabled的值永远不会改变,它保持为真,即按钮始终保持启用状态,或者如果我更改&gt;签名,按钮始终处于禁用状态。有什么建议吗?
答案 0 :(得分:7)
IsSearchCriteriaHasValue
需要引发更改的事件,您可以使用INotifyPropertyChanged
界面执行此操作:
public class Customer : INotifyPropertyChanged
{
// INotifyPropertyChanged members
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(PropertyChangedEventArgs e)
{
if (PropertyChanged != null)
{
PropertyChanged(this, e);
}
}
// Your property
private string _Name;
public string Name
{
get
{
return _Name;
}
set
{
_Name = value;
OnPropertyChanged(new PropertyChangedEventArgs("Name"));
}
}
}
答案 1 :(得分:2)
您可以为按钮编写触发器(SearchBox查看UI控件)
<Style TargetType="Button"> <Setter Property="IsEnabled" Value="True" /> <Style.Triggers> <DataTrigger Binding="{Binding Selection.Count, ElementName=SearchBox}" Value="0"> !-- You can use convertor also <Setter Property="IsEnabled" Value="False" /> </DataTrigger> </Style.Triggers> </Style> </Button.Style> </Button>
答案 2 :(得分:1)
它与XAML没有问题,它的通知问题。我希望你知道INotifyProperty接口的NotifyPropertyChanged事件。只有在ViewModel中为属性触发了该属性时,UI才会获取通知并对其进行更新。
如果SearchBox.Selection计数发生变化,它不会触发任何IsSearchCriteriaHasValue属性的通知,表明它已被更改并且UI应该更新。
让我们说SearchBox.Selection绑定到observableCollection并且集合发生变化,然后订阅observableCollection以进行添加/删除然后触发NotifyPropertyChanged("IsSearchCriteriaHasValue")
;那里。
答案 3 :(得分:1)
绑定适用于属性更改事件。您的ViewModel
应该实现INotifyPropertyChanged
界面。
https://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged(v=vs.110).aspx
一个例子:
// This form demonstrates using a BindingSource to bind
// a list to a DataGridView control. The list does not
// raise change notifications. However the DemoCustomer type
// in the list does.
public partial class Form1 : Form
{
// This button causes the value of a list element to be changed.
private Button changeItemBtn = new Button();
// This DataGridView control displays the contents of the list.
private DataGridView customersDataGridView = new DataGridView();
// This BindingSource binds the list to the DataGridView control.
private BindingSource customersBindingSource = new BindingSource();
public Form1()
{
InitializeComponent();
// Set up the "Change Item" button.
this.changeItemBtn.Text = "Change Item";
this.changeItemBtn.Dock = DockStyle.Bottom;
this.changeItemBtn.Click +=
new EventHandler(changeItemBtn_Click);
this.Controls.Add(this.changeItemBtn);
// Set up the DataGridView.
customersDataGridView.Dock = DockStyle.Top;
this.Controls.Add(customersDataGridView);
this.Size = new Size(400, 200);
}
private void Form1_Load(object sender, EventArgs e)
{
// Create and populate the list of DemoCustomer objects
// which will supply data to the DataGridView.
BindingList<DemoCustomer> customerList = new BindingList<DemoCustomer>();
customerList.Add(DemoCustomer.CreateNewCustomer());
customerList.Add(DemoCustomer.CreateNewCustomer());
customerList.Add(DemoCustomer.CreateNewCustomer());
// Bind the list to the BindingSource.
this.customersBindingSource.DataSource = customerList;
// Attach the BindingSource to the DataGridView.
this.customersDataGridView.DataSource =
this.customersBindingSource;
}
// Change the value of the CompanyName property for the first
// item in the list when the "Change Item" button is clicked.
void changeItemBtn_Click(object sender, EventArgs e)
{
// Get a reference to the list from the BindingSource.
BindingList<DemoCustomer> customerList =
this.customersBindingSource.DataSource as BindingList<DemoCustomer>;
// Change the value of the CompanyName property for the
// first item in the list.
customerList[0].CustomerName = "Tailspin Toys";
customerList[0].PhoneNumber = "(708)555-0150";
}
}
// This is a simple customer class that
// implements the IPropertyChange interface.
public class DemoCustomer : INotifyPropertyChanged
{
// These fields hold the values for the public properties.
private Guid idValue = Guid.NewGuid();
private string customerNameValue = String.Empty;
private string phoneNumberValue = String.Empty;
public event PropertyChangedEventHandler PropertyChanged;
// This method is called by the Set accessor of each property.
// The CallerMemberName attribute that is applied to the optional propertyName
// parameter causes the property name of the caller to be substituted as an argument.
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
// The constructor is private to enforce the factory pattern.
private DemoCustomer()
{
customerNameValue = "Customer";
phoneNumberValue = "(312)555-0100";
}
// This is the public factory method.
public static DemoCustomer CreateNewCustomer()
{
return new DemoCustomer();
}
// This property represents an ID, suitable
// for use as a primary key in a database.
public Guid ID
{
get
{
return this.idValue;
}
}
public string CustomerName
{
get
{
return this.customerNameValue;
}
set
{
if (value != this.customerNameValue)
{
this.customerNameValue = value;
NotifyPropertyChanged();
}
}
}
public string PhoneNumber
{
get
{
return this.phoneNumberValue;
}
set
{
if (value != this.phoneNumberValue)
{
this.phoneNumberValue = value;
NotifyPropertyChanged();
}
}
}
}
}
答案 4 :(得分:-1)
绑定适用于属性更改事件。您的ViewModel应该实现INotifyPropertyChanged
接口。而且你需要在属性集中提升属性更改事件。或者,您只需使用delegate command
并在CanExecute方法中写入启用禁用逻辑。
请参阅此链接以获取更多信息
http://www.codeproject.com/Questions/179129/MVVM-Enable-Disable-button-via-a-PropertyChanged-e